Switched beam antenna architecture

ABSTRACT

A multiple beam array antenna system comprises a plurality of radiating elements provided from stripline-fed open-ended waveguide coupled to a Butler matrix beam forming network. The Butler matrix beam forming network is coupled to a switched beam combining circuit. The antenna can be fabricated as a single Low Temperature Co-fired Ceramic (LTCC) circuit.

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. ProvisionalApplication No. 60/226,160, filed on Aug. 16, 2000 and is herebyincorporated herein by reference in its entirely.

STATEMENTS REGARDING FEDERALLY SPONSORED RESEARCH

[0003] Not applicable.

FIELD OF THE INVENTION

[0004] This invention relates to antenna elements and more particularlyto an antenna element for use in an array antenna.

BACKGROUND OF THE INVENTION

[0005] As is known in the art, there is an increasing trend to includeradar systems in commercially available products. For example, it isdesirable to include radar systems in automobiles, trucks boats,airplanes and other vehicle. Such radar systems must be compact andrelatively low cost.

[0006] Furthermore, some applications have relatively difficult designparameters including restrictions on the physical size of the structurein addition to minimum operational performance requirements. Suchcompeting design requirements (e.g. low cost, small size, highperformance parameters) make the design of such radar systems relativelychallenging. Among, the design challenges is a the challenge to providean antenna system which meets the design goals of being low cost,compact and high performance.

[0007] In automotive radar systems, for example, cost and sizeconsiderations are of considerable importance. Furthermore, in order tomeet the performance requirements of automotive radar applications,(e.g. coverage area) an array antenna is required. Some antenna elementswhich have been proposed for use in antenna arrays manufactured forautomotive radar applications include patch antenna elements, printeddipole antenna elements and cavity backed patch antenna elements. Eachof these antenna elements have one or more drawbacks when used in anautomotive radar application.

[0008] For example, patch antenna elements and cavity backed patchantenna elements each require a relatively large amount of substratearea and thickness. Array antennas for automotive applications, however,are have only a limited amount of area for reasons of compactness andcost. Thus, antenna elements which can operate in a high density circuitare required. Printed dipole antennas can operate in a high densitycircuit environment, however, array antennas provided from printeddipole antenna elements give rise to “blind spots” in the antennaradiation pattern.

[0009] It would, therefore, be desirable to provide an antenna elementwhich is compact, which can operate in a high density circuitenvironment, which is relatively low cost and which can be used toprovide an array antenna having relatively high performancecharacteristics.

SUMMARY OF THE INVENTION

[0010] In accordance with the present invention, an antenna elementincludes a cover layer disposed over a radiator layer having a firstground plane disposed thereon with the ground plane having an aperturetherein. The radiator layer is disposed over a feed circuit layer whichhas a second ground plane disposed thereon. A cavity is provided in theradiator and feed circuit layers by disposing a plurality of via holesbetween the first and second ground plane layers. An antenna elementfeed couples energy between the feed circuit and the antenna element. Afeed circuit couples energy between the antenna element feed and abutler matrix and is provided as an elevation feed which is interlacedbetween each of the antenna elements. With this particular arrangement,a compact slotted antenna element which utilizes a stripline-fed openended dielectric filled cavity is provided. In one embodiment, theantenna element is provided from LTTC substrates on which the. Multipleantenna elements can be disposed to provide a compact array antennacapable of switching between multiple antenna beams. The antenna elementof the present invention requires only five layers and thus can beprovided as a relatively low cost antenna. The radiator layers can beprovided having capacitive windows formed therein for tuning the antennaelement. By providing the feed circuit as an elevation feed which isinterlaced between each of the antenna elements, a compact antenna whichcan operate in a densely packed environment is provided. A multiple beamarray antenna was designed to radiate at 24 GHz. The entire antenna wasfabricated in a single Low Temperature Co-fired Ceramic (LTCC) circuit.The design of the antenna included the radiating element (stripline-fedopen-ended waveguide), the beam forming network (Butler Matrix),radiator feed circuit, quadrature hybrid, power dividers, and interlayertransitions.

[0011] In accordance with a further aspect of the present invention, anarray antenna comprises a plurality of slotted antenna elements, each ofwhich utilizes a stripline-fed open ended dielectric filled cavity. Withthis particular arrangement, a compact array antenna which can providemultiple beams is provided. The antenna can be used in a sensor utilizedin an automotive radar application. In a preferred embodiment, thesensor includes a transmit and a receive antenna. In a preferredembodiment, the transmit and receive antennas are provided as abi-static antenna pair disposed on a single substrate. In otherembodiments, however, a monostatic arrangement can be used.

[0012] In accordance with a still further aspect of the presentinvention, a switched beam antenna system includes a plurality ofantenna elements, a butler matrix having a plurality of antenna portsand a plurality of switch ports with each of the antenna ports coupledto a respective one of the plurality of antenna elements and a switchcircuit having an input port and a plurality of output ports each of theswitch output ports coupled to a respective one of the plurality ofswitch ports of the butler matrix. With this particular arrangement, amultiple beam switched beam antenna system is provided. By providing theantenna elements from a single Low Temperature Co-fired Ceramic (LTCC)substrate, the antenna system can be provided as a compact antennasystem. In a preferred embodiment the radiating element are providedfrom stripline-fed open-ended waveguide fabricated in the LTTC substrateand the Butler matrix, radiator feed circuit, quadrature hybrid, powerdividers, and interlayer transitions are also provided in the LTTCsubstrate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The foregoing features of this invention, as well as theinvention itself, may be more fully understood from the followingdescription of the drawings in which:

[0014]FIG. 1 is a block diagram of a radar system;

[0015]FIG. 2 is a block diagram of an automotive near object detection(NOD) system including a plurality of radar systems;

[0016]FIG. 3 is a perspective view of a side object detection (SOD)system;

[0017]FIG. 4 is block diagram of a switched beam antenna system;

[0018]FIG. 5 is a block diagram of a switched beam forming circuit;

[0019]FIG. 6 is a block diagram of a Butler matrix beam forming circuitcoupled to a plurality of antenna elements;

[0020]FIG. 7 is a plot of a Butler matrix beams;

[0021]FIG. 7A is a plot of antenna system beams provided by combiningpredetermined ones of the Butler matrix beams;

[0022]FIG. 7B is a plot of antenna system beams provided by combiningpredetermined ones of the Butler matrix beams;

[0023]FIG. 8 is a diagrammatic view of a detection zone which can beprovided by the SOD system of FIGS. 2A and 11;

[0024]FIG. 8A is a diagrammatic view of a second detection zone whichcan be provided by the SOD system of FIGS. 3 and 11;

[0025]FIG. 9 is a top view of an array aperture formed by a plurality ofantenna elements;

[0026]FIG. 10 is an exploded perspective view of an antenna element;

[0027]FIG. 11 is a cross-sectional view of taken across lines 11-11 ofthe antenna element of FIG. 10; and

[0028]FIG. 12 is a detailed block diagram of a SOD system.

DETAILED DESCRIPTION OF THE INVENTION

[0029] Referring to FIG. 1, a radar system 10 includes an antennaportion 14, a microwave portion 20 having both a transmitter 22 and areceiver 24, and an electronics portion 28 containing a digital signalprocessor (DSP) 30, a power supply 32, control circuits 34 and a digitalinterface unit (DIU) 36. The transmitter 22 includes a digital rampsignal generator for generating a control signal for a voltagecontrolled oscillator (VCO), as will be described.

[0030] The radar system 10 utilizes radar technology to detect one ormore objects, or targets in the field of view of the system 10 and maybe used in various applications. In the illustrative embodiment, theradar system 10 is a module of an automotive radar system (FIG. 2) and,in particular, is a side object detection (SOD) module or system adaptedfor mounting on an automobile or other vehicle 40 for the purpose ofdetecting objects, including but not limited to other vehicles, trees,signs, pedestrians, and other objects which can be located proximate apath on which the vehicle is located. As will be apparent to those ofordinary skill in the art, the radar system 10 is also suitable for usein many different types of applications including but not limited tomarine applications in which radar system 10 can be disposed on a boat,ship or other sea vessel.

[0031] The transmitter 22 operates as a Frequency Modulated ContinuousWave (FMCW) radar, in which the frequency of the transmitted signallinearly increases from a first predetermined frequency to a secondpredetermined frequency. FMCW radar has the advantages of highsensitivity, relatively low transmitter power and good range resolution.However, it will be appreciated that other types of transmitters may beused.

[0032] Control signals are provided by the vehicle 40 to the radarsystem 10 via a control signal bus 42 and may include a yaw rate signalcorresponding to a yaw rate associated with the vehicle 40 and avelocity signal corresponding to the velocity of the vehicle. The DSP 30processes these control signals and radar return signals received by theradar system 10, in order to detect objects within the field of view ofthe radar system, as will be described in conjunction with FIGS. 10-16.The radar system 10 provides to the vehicle one or more output signalscharacterizing an object within its field of view via an output signalbus 46 to the vehicle. These output signals may include a range signalindicative of a range associated with the target, a range rate signalindicative of a range rate associated with the target and an azimuthsignal indicative of the azimuth associated with the target relative tothe vehicle 40. The output signals may be coupled to a control unit ofthe vehicle 40 for various uses such as in an intelligent cruise controlsystem or a collision avoidance system.

[0033] The antenna assembly 14 includes a receive antenna 16 forreceiving RF signals and a transmit antenna 18 for transmitting RFsignals. The radar system 10 may be characterized as a bistatic radarsystem since it includes separate transmit and receive antennaspositioned proximate one another. The antennas 16, 18 provide multiplebeams at steering angles that are controlled in parallel as to point atransmit and a receive beam in the same direction. Various circuitry forselecting the angle of the respective antennas 16, 18 is suitable,including a multi-position switch.

[0034] Referring now to FIG. 2, an illustrative application for theradar system 10 of FIG. 1 is shown in the form of an automotive nearobject detection (NOD) system 50. The NOD system 50 is disposed on avehicle 52 which may be provided for example, as an automotive vehiclesuch as car, motorcycle, or truck, or a marine vehicle such as a boat oran underwater vehicle or as an agricultural vehicle such as a harvester.In this particular embodiment, the NOD system 50 includes aforward-looking sensor (FLS) system 54 which maybe of the type describedin U.S. Patent, an electro-optic sensor (EOS ) system 56, a plurality ofside-looking sensor (SLS) systems 58 or equivalently side objectdetection (SOD) systems 58 and a plurality of rear-looking sensor (RLS)systems 60. In the illustrative embodiment, the radar system 10 of FIG.1 is a SOD system 58.

[0035] Each of the FLS, EOS, SLS, and RLS systems is coupled to a sensorprocessor 62. In this particular embodiment, the sensor processor 62 isshown as a central processor to which each of the FLS, EOS, SLS, and RLSsystems is coupled via a bus or other means. It should be appreciatedthat in an alternate embodiment, one or more of the FLS, EOS, SLS, andRLS systems may include its own processors, such as the DSP 30 of FIG.1, to perform the processing described below. In this case, the NODsystem 100 would be provided as a distributed processor system.

[0036] Regardless of whether the NOD system 50 includes a single ormultiple processors, the information collected by each of the sensorsystems 54, 56, 58 60 is shared and the processor 62 (or processors inthe case of a distributed system) implements a decision or rule tree.The NOD system 50 may be used for a number of functions including butnot limited to blind spot detection, lane change detection, pre-armingof vehicle air bags and to perform a lane stay function. For example,the sensor processor 62 may be coupled to the airbag system 64 of thevehicle 52. In response to signals from one or more of the FLS, EOS,SLS, and RLS systems, the sensor processor 62 determines whether it isappropriate to “pre-arm” the airbag of the vehicle. Other examples arealso possible.

[0037] The EOS system 56 includes an optical or IR sensor or any othersensor which provides relatively high resolution in the azimuth plane ofthe sensor. The pair of RLS systems 60 can utilize a triangulationscheme to detect objects in the rear portion of the vehicle. The FLSsystem 54 may be of the type described in U.S. Pat. No. 5,929,802entitled Automotive Forward Looking Sensor Architecture, issued Jul. 27,1999, assigned to the assignee of the present invention, andincorporated herein by reference. It should be appreciated that each ofthe SLS and RLS sensors 58, 60 may be provided having the same antennasystem.

[0038] Each of the sensor systems is disposed on the vehicle 52 suchthat a plurality of coverage zones exist around the vehicle. Thus, thevehicle is enclosed in a cocoon-like web or wrap of sensor zones. Withthe particular configuration shown in FIG. 2, four coverage zones 66a-66 d are used. Each of the coverage zones 66 a-66 d utilizes one ormore RF detection systems. The RF detection system utilizes an antennasystem which provides multiple beams in each of the coverage zones 66a-66 d. In this manner, the particular direction from which anotherobject approaches the vehicle or vice-versa can be found.

[0039] It should be appreciated that the SLS, RLS, and the FLS systemsmay be removably deployed on the vehicle. That is, in some embodimentsthe SLS, RLS, and FLS sensors may be disposed external to the body ofthe vehicle (i.e. on an exposed surface of the vehicle body), while inother systems the SLS, RLS, and FLS systems may be embedded into bumpersor other portions of vehicle (e.g. doors, panels, quarter panels,vehicle front ends, and vehicle rear ends). It is also possible toprovide a system which is both mounted inside the vehicle (e.g., in thebumper or other location) and which is also removable. The system formounting can be of a type described in U.S. patent application Ser. No.09/______, entitled Portable Object Detection System and System filedAug. 16, 2001 or in U.S. patent application Ser. No. 09/______, entitledTechnique for Mounting a Radar System on a Vehicle filed Aug. 16,2001,each of the above-identified patent applications assigned to theassignee of the present invention, and each incorporated herein byreference.

[0040] Referring now to FIG. 3, a side object detection (SOD) system 70includes a housing 72 in which the SOD electronics are disposed. Aportion of the housing has here been removed to reveal a singlesubstrate 76 on which a plurality of antenna elements 77 are disposed. Apreferred antenna array and antenna element will be described inconjunction with FIGS. 9-11 below. In this particular embodiment, thesubstrate 76 is provided as Low Temperature Co-fired Ceramic (LTCC)substrate 76. As will be described in detail below in conjunction withFIGS. 10 and 11, the single substrate 76 can be provided from aplurality of LTCC layers.

[0041] Also provided in the LTTC substrate 76 is a Butler matrix beamforming circuit, a radiator feed circuit coupled to the antenna elements75, a plurality of quadrature hybrid and power divider circuits as wellas interlayer transition circuits.

[0042] In one embodiment, the housing 72 for the antenna is providedfrom an injection molded plastic PBT (polybutylene terephthalate) havinga relative dielectric constant (∈_(r)) of about 3.7. The housing 72includes a cover 73. One characteristic of cover 73 that affects antennaperformance is the cover thickness. In a preferred embodiment, the coverthickness is set to one-half wavelength (0.5λ) as measured in thedielectric. At an operating frequency of about 24 GHz, this correspondsto a cover thickness of about 0.125 inch. The antenna aperture ispreferably spaced from the cover 73 by a distance D (measure from theantenna aperture to an inner surface of the cover 73) which correspondsto a distance slightly less than about 0.5 λ as measured in air. At anoperating frequency of about 24 GHz, this corresponds to about 0.2 inch.Other dimensions of the cover 73 are selected based on structure andmanufacturing. The housing 72 is provided having a recess region inwhich the substrate 76 is disposed. The housing may be of the typedescribed in co-pending U.S. patent application Ser. No. 09/______,entitled Highly Integrated Single Substrate MMW Multi-Beam Sensor, filedAug. 16, 2001, assigned to the assignee of the present invention andincorporated herein by reference in its entirety.

[0043] In one embodiment, the antenna is built using Ferro's A6-M LTCCtape. The tape is provided havibg a thickness of about 0.010 inchpre-fired and 0.0074 inch post-fired and a dielectric constant of about5.9. The LTTC tape has a loss characteristic at 24 GHz of 1.0 dB(morelike 1.1 dB) per inch for a 0.0148 inch ground plane spacing.

[0044] LTCC was chosen for this antenna for a variety of reasonsincluding but not limited to its potential for low cost in high volumeproduction. Furthermore, LTCC allows compact circuit design and iscompatible technology (at this frequency) for multi-layer circuitshaving relativley large quantities of reliable, embedded vias(approximately 1200 vias in oneparticualr embodiment of this antenna).Surface-mount devices can also be integrated with LTCC.

[0045] Referring now to FIG. 4, a switched beam antenna system includesan antenna 80 having a plurality of antenna elements 82. Each of theantenna elements 82 are coupled through a respective one of a pluralityof elevation distribution networks 84 a-84 h to a respective one of aplurality of output ports 86 a-86 h of a Butler matrix beam formingnetwork 88. As will be described in conjunction with FIGS. 5-7 below, asignal fed to predetermined ones of the input or beam port 88 a-88 hresults in the antenna forming a beam which appears in a different beamlocation in an azimuth plane. Each of the elevation distributionnetworks 84 is comprised of a first two-to-one (2:1) power divider 90,which splits the power equally to two radiator feed circuits 92 a, 92 b.

[0046] In one embodiment, the radiator feed circuit is provided from acorporate feed that provides half of the amplitude distribution inelevation. Each feed circuit 92 a, 92 b is coupled, respectively, tothree “radiating elements” or more simply “radiators” through signalpaths having differential line lengths. These differential line lengthsprovide the appropriate phase shift for the elevation beam steer.

[0047] The Butler matrix input ports are coupled to output ports of aswitched beam combining circuit 90 having a first plurality of switchports 92 a-92 h coupled to corresponding ones of the Butler matrix ports88 a-88 h and a common port 94 at which combined beams are provided aswill be described below.

[0048] The ports 88 a-88 h of the Butler matrix 88 represent differentantenna beam locations. These beams are independent and aresimultaneously available. The location of the beams with respect toButler port location is given in FIG. 7 where reference numbers 120a-120 h represent the relative locations of the beams in space, and thebeam numbers 1-8 (designated by reference numerals 121 a-121 h in FIG.7) refer to the Butler input beam port numbers as given in FIG. 6 andsimilarly in FIG. 5, designated with reference numbers 102 a-102 h. Itshould be noted that adjacent beams (in space) are always located onopposite halves of the Butler input beam ports (left half of beamsports, 1, 2, 3 and 4 and right half of beam ports 5, 6, 7 and 8). Thecombination of adjacent orthogonal beams will give a resulting beamhaving a cosine aperture distribution, and therefore lower sidelobelevels. By placing a 4-way switch (such as switches 105, 106 in FIG. 5)each half of the Butler input beam ports access to any adjacent pair ofbeams is realized. The inputs of the two 4-way switches 105 a and 106 a(FIG. 5) are then combined through an equal power divider 108. In thisway, the single input to the power divider 108 a is connected to one ofseven combined beams (designated as 124 a-124 g in FIG. 7A). The beamcombinations in FIG. 7A, are represented by the numbered pairs (2,6),(6,4), (4,8), (8,1), (1,5), (5,3), (3,7). That is, beam 124 a (FIG. 7A)is provided from the combination of beams 2 and 6 represented as (2, 6).Similarly, beam 124 b (FIG. 7A) is provided from the combination ofbeams 6 and 4 represented as (6, 4); beam 124 c (FIG. 7A) is providedfrom the combination of beams 4 and 8 represented as (4, 8); beam 124 d(FIG. 7A) is provided from the combination of beams 8 and 1 representedas (8, 1); beam 12 e (FIG. 7A) is provided from the combination of beams1 and 5 represented as (1, 5); beam 124 f (FIG. 7A) is provided from thecombination of beams 5 and 3 represented as (5, 3); and beam 124 g (FIG.7A) is provided from the combination of beams 3 and 7 represented as (3,7).

[0049] These numbered pairs also represent the switch location for leftand right switches 105, 106 (FIG. 5), respectively. For example, ifswitch 105 is set to select port 1 designated as reference number 102 ain FIG. 5) (i.e. provide a low impedance signal path between port 1 andswitch port 105 a) and switch 106 is set to select port 8 designated byreference number 102 h in FIG. 5. The resulting combined beam at powerdivider port 108 a is beam 8, 1 which is the center beam.

[0050] Referring now to FIG. 5, a Butler matrix beam forming network 98is shown having a plurality of antenna element ports 100 a-100 h (whichmay correspond, for example, to ports 86 a-86 h of FIG. 4) and aplurality of switch ports 102 a-102 h (which may correspond, forexample, to ports 88 a-88 h of FIG. 4). The switch ports 102 a-102 h arecoupled through transmission lines 103 a-103 h to a switched beamcombining circuit 104. As is known, the port phasing for Butlers have180° phase difference and the curved signal paths 103 a, 103 c represent180° differential line lengths required to bring all of the ports inphase with each other. The switched beam combining circuit 104 is hereprovided from a pair of single pole four throw switches 105, 106, eachof the switches 105, 106 having a common port 105 a, 106 a coupled tothe output port of a power divider circuit 108. The power dividercircuit 108 is provided such that a signal fed to an input port 108 ahas an equal phase equal power level at the output ports 108 b, 108 c.

[0051] Referring now to FIG. 6, a plurality of antenna elements 110a-110 h are coupled to ports 100 a-100 h of a Butler matrix beam formingnetwork 112. The Butler matrix beam forming network 112 is here shownprovided from a plurality of power divider circuits 114. The circuits114 are provided as quadrature, or 90°, stripline ring hybrids which arecoupled as shown to provide the Butler Matrix Circuit. These hybridshave a 3 dB power split with a 90° phase difference in the outputs ofthe through and coupled arms. The Butler matrix is a lossless beamforming network that forms orthogonal beams at fixed locations. The beamlocations are a function of the spacing of the antenna elements in anantenna array (referred to as an array lattice spacing). In thisparticular embodiment, the Butler matrix 112 uses quadrature hybridcircuits 114 and fixed phase shifts to form the multiple beams. As willbe explained in further detail below, the fixed phase shifts areprovided from differential line lengths 115 where the path lengths areindicated by the 2n's, 3n's and ln's in FIG. 6, where n=/8 radians.Other techniques for providing the fixed phase shifts can also be used.

[0052] Typically, for narrow bandwidths, the fixed phase shifts aresimply differential line lengths. The unit of phase shift is π/8 radiansor λ/16. There are 2^(N) beams. Butler gives the following equation tocalculate the beam locations:${{beamloc}(M)}:={a\quad {{\sin \left\lbrack {\frac{\lambda}{N \cdot d} \cdot \left( {M - \frac{1}{2}} \right)} \right\rbrack} \cdot \frac{180}{\pi}}}$

[0053] where:

[0054] λ is the wavelength of the center frequency;

[0055] N is the number of elements;

[0056] d is the element spacing; and

[0057] M is the beam number.

[0058] Referring now to FIG. 7, in this particular embodiment, theButler matrix forms eight beams 120 a-120 h. That is, by providing aninput signal to one of the Butler matrix input ports 112 a-112 h, theantenna 110 produces a corresponding one of the beams 120 a-120 h. Thecalculations for determining the beam locations can be found using theequations below: $\begin{matrix}{\quad {{{Wavelength}\quad ({inches})}:}} & {\quad {\lambda:=\frac{11.81}{24}}} \\{\quad {{Number}\quad {of}\quad {{Elements}:}}} & {\quad {N:=8}} \\{\quad {{{Element}\quad {Spacing}\quad ({Azimuth})}:}} & {\quad {d:={.223}}} \\{\quad {{{Beam}\quad {Location}\quad ({Degrees})}:}} & {\quad {{{beamloc}(M)}:={a\quad {{\sin \left\lbrack {\frac{\lambda}{N \cdot d} \cdot \left( {M - \frac{1}{2}} \right)} \right\rbrack} \cdot \frac{180}{\pi}}}}} \\{\quad {{Beam}\quad {{Number}:}}} & {\quad {M:={1\quad \ldots \quad \frac{N}{2}}}}\end{matrix}$

[0059] If the array is provided having an array lattice spacing of0.223″ in azimuth, the beam locations shown in FIG. 7 are provided. Inone embodiment, the differential line length value, n is selected to be{fraction (1/16)}λ which corresponds to 0.0127 inch at a frequency of 24GHz. FIG. 7 also illustrates which beam-ports in FIG. 6 produce whichbeams.

[0060] Referring now to FIG. 7A, a calculated antenna radiation pattern122 includes seven beams 124 a-124 g which can be used in a radarsystem. The seven beams are provided by combining predetermined ones ofthe eight beams formed by the Butler Matrix as discussed above. Adjacentbeams (e.g. beams 120 a, 120 b from FIG. 7) can be combined to producebeam 124 a as illustrated in FIG. 7A. Since beams out of a Butler Matrixby definition are orthogonal, combining beams in azimuth produces acos(θ) taper with a peak sidelobe level of 23 dB (with respect to thebeam maximum).

[0061] The locations of the combined beams are listed in the Tablebelow. TABLE Combined Beam Beam Location 8, 1 0 4, 8 & 1, 5 +/−16 6, 4 &5, 3 +/−34 2, 6 & 3, 7 +/−57

[0062] In elevation, there is also a 25 dB Chebyshev taper and a 15°beam steer.

[0063] Referring now to FIG. 7B, the resultant combined beam arrayfactor is shown The combined beams are errorless contours in U-V spacewith a 20 dB floor. They assume a cos(θ) element factor. The plots are arepresentation of the seven combined beams in azimuth with the 15° beamsteer in elevation.

[0064] It should be appreciated that producing the cos(θ) taper inazimuth with the adjacent beam combining was a cost driven designchoice. Instead, the taper could have been produced using attenuators.However, these would have required the use of embedded resistors in theLTCC circuit. Using embedded resistors on an LTCC tape layer would addanother processing step in the manufacture of the LTCC circuit.Therefore, using attenuators to produce the azimuth distribution wouldhave increased the cost of the antenna. Moreover, the technique of thepresent invention simplifies the switch network by eliminating a 2-wayswitch.

[0065] Referring now to FIGS. 8 and 8A, two different examples of sidedetection zones are shown. In FIG. 8, a vehicle 129 has a maximumdetection zone 130 disposed thereabout. The maximum detection zone 130is defined by a detection zone boundary 131 In this example, the maximumdetection zone boundary 130 is provided having a trapezoidal shape. Anexemplary SOD system provides seven azimuthal beams 132 a-132 g eachwith a different maximum detection range, as indicated by the shadedregion, and as determined by a detection algorithm that operates uponthe beam echoes. The algorithmic control of the maximum detection rangeof each of the eight beams defines the shape of an actual maximumdetection zone boundary 134 versus a specified nominal detection zoneboundary 136. The manner in which an object is detected is described inco-pending U.S. Pat. application Ser. No. 09/______, entitled RadarDetection Method and Apparatus, filed Aug. 16, 2001 assigned to theassignee of the present invention and incorporated herein by referencein its entirety.

[0066] The exemplary SOD system of FIGS. 8 and 8A, has seven beams, eachwith a beam width of approximately fifteen degrees and with a totalazimuth scan of about one hundred fifty degrees. It will be recognizedby one of ordinary skill in the art that other numbers of beams (e.g.fewer or more than seven) and scan angles are possible without departingfrom the present invention. The particular number of antenna beams touse in a particular application is selected in accordance with a varietyof factors including but not limited to shape of coverage zone, size ofcoverage zone, required Azimuth resolution, complexity and cost.

[0067] Referring now to FIG. 8A, a boundary 140 having a substantiallyrectangular shape defines a detection zone 142 about a vehicle 144.Again, an exemplary system provides seven azimuthal antenna beams 146a-146 g each of the antenna beams 146 a-146 g having a different maximumdetection range 148 as indicated by shading. The maximum detectionranges 148 being different from beams 132 a-132 g (FIG. 8) so as to forma different actual maximum detection zone.

[0068] Referring now to FIG. 9, an array antenna 150 having a length Land width W includes a transmit array 152 and a receive array 154. Eachof the arrays 152, 154 includes eight rows 156 a-156 g and six columns158 a-158 f. Thus each of the transmit and receive arrays 152, 154 haveforty-eight radiating elements (or more simply “radiators” or“elements”), generally denoted 160, with eight elements in azimuth andsix elements in elevation.

[0069] As will be described in detail in conjunction with FIGS. 10 and11, each radiating element 160 is a stripline-fed open-ended cavity inLTCC. The cavity is formed in the LTCC using embedded vias, generallydenoted 162, that create the “cavity walls.” Each of the arrays 152, 154have a rectangular lattice spacing: 0.223″ (azimuth)×0.295″ (elevation).The azimuth spacing is driven by the Butler matrix to yield desired beamlocations which provided desired detection zones. The elevation spacingis driven by an elevation beamwidth requirement and the maximum spacingneeded to avoid a cover induced scan blindness.

[0070] In an automotive radar application, the antenna is enclosed in aplastic housing and will radiate through the housing cover (e.g. asshown in FIG. 3). In one embodiment, the housing cover can beincorporated into the radiator design. In a preferred embodiment,however, the antenna radiates through a housing cover spaced aboutone-half wavelength from the antenna aperture as shown in FIG. 3. Inthis approach, the antenna, can have an antenna cover disposedthereover, but the cover can be made of additional layer of LTCC (e.g.as represented by layer 176 in FIG. 10).

[0071] Referring now to FIG. 10, in which like elements of FIG. 9 areprovided having like reference designations, a radiating element 170which may be used for example in the antennas described in conjunctionwith FIGS. 2A, 3, 5, 8, 9 and 11 includes a ground plane layer 172having first and second opposing surfaces with a ground plane 173disposed over the second surface thereof. A plurality of radiatinglayers 174 are disposed over the second surface of the ground planelayer 172. Each of the radiating layers 174 has an antenna structureincluded thereon as will be described below in detail below. Suffice ithere to say that structures on each of the radiating layers 174 areappropriately aligned relative to the ground plane 173.

[0072] An antenna element cover layer 176 is disposed over the radiatinglayers 174. In one embodiment, the element cover layer 176 for theantenna 170 is incorporated into the radiator 170. In one particularembodiment in which the element operates at a frequency of about 24 GHz,the element cover layer 176 is provided having a thickness of about0.038 inches and a dielectric constant of about 3.5 and is used to“tune” the radiator 170 (i.e. the cover 176 is utilized to help providethe antenna element 170 having an appropriate response to signals in adesired frequency range.

[0073] In another embodiment, to be described below in conjunction withFIG. 10, the cover layer 176 is provided from LTCC having a thickness ofabout 22.2 mils. In this embodiment, the cover layer can be providedfrom three 10 mil (prefired) tape layers (e.g. layers 218-222 in FIG.11).

[0074] In the embodiment of FIG. 9, the radiating layers are providedfrom four layers 178-184. Each of the radiating layers 178-184 areprovided as LTCC tape layers. The layers are provided having a thicknessof about 10 mil (prefired) and about 7.4 mil(post fired) with a nominal∈_(r) of about 5.9. and a loss tangent typically of about 0.002.

[0075] Layer 178 is provided having a conductive strip 188 disposedthereon which corresponds to an antenna element feed circuit 188. Thelayer 180 is provided having a conductive material 190 disposed thereonwhich corresponds to a ground plane 190. Thus, feed circuit 188 isdisposed between upper and lower ground planes and thus layer 178corresponds to a stripline feed layer 178.

[0076] The ground plane 190 is provided having an aperture 192 thereinand thus layer 180 corresponds to both a ground plane layer and acapacitive layer 180. Layer 182 is provided having a conductive trace191 disposed thereon through which vias 160 are disposed. The conductivetrace 191 forms an aperture 193. Disposed over the layer 182 is thelayer 184 which is provided having a ground plane 194 disposed on a topor second surface thereof. The ground plane has a portion thereofremoved to form an aperture 196.

[0077] Conductive vias 160 pass through each of the layers 172 and178-184 to form a cavity. Thus, the ground plane layer 172, radiatinglayers 174 (and associated structures disposed on the radiating layers174) and cover layer 176 form the radiating element 170 as astripline-fed open-ended cavity formed in LTCC. The cavity is formed inthe LTCC by the embedded vias 160 which provide a continuous conductivepath from a first or top surface of aperture layer 184 to a second ortop surface of the ground plane layer 172 and is fed by the striplineprobe 188.

[0078] In one particular embodiment the cavity is provided having alength of 0.295 inches, a width of 0.050 inches and a height of 0.0296inches (0.295″×0.050″×0.0296″). The capacitive windows 192 were used onthe aperture and as internal circuit layers for tuning the radiator.

[0079] In this particular embodiment, the design of the radiator 170 wasdriven by the desire to reduce the number of LTCC layers, and here thecost. Due to the low cost requirement of the antenna, the antenna itselfwas specified to have a maximum number of eight LTCC tape layers. Asdescribed above in conjunction with FIG. 5, the Butler Matrix circuit iscomprised of four LTCC tape layers or two stripline circuit layers. Dueto the size and circuit layout of the Butler Matrix, it was necessary tosplit the beam forming network between two stripline circuit layers orfour LTCC tape layers. Therefore, there were four LTCC tape layersavailable for the radiator. In addition, these remaining four LTCCcircuit layers also needed to include the elevation distributionnetwork. This resulted in an RF circuit having a relatively high densityof circuits on those layers.

[0080] In this particular embodiment, the antenna element 170 includesthe reactive apertures or windows 192, 193 and 196 which are used toprovide the radiating element 170 having a desired impedance match tofree space impedance. The reactive apertures 192, 193, 196 as well asthe element cover 176 are used to match the impedance of the feed line188 to free space impedance. Thus, the radiating element 170 includestuning structures on a plurality of different layers, here threedifferent layers of the radiator, which can be used to provide theantenna element 170 having a desired impedance.

[0081] The cover 176 was provided from LTTC and was utilized as a tuningstructure as well. However, dielectric covers are often associated withscan blindness phenomena in arrays. An analysis of the scan reflectioncoefficient for different cover thicknesses was performed to ensure thatscan blindness effects would not hinder the performance of the antenna.

[0082] The results of the scan blindness analysis for a variety of coverthicknesses for scan reflection coefficient (due to the cover 176) vs.the scan angle in degrees revealed that a preferred range of coverthicknesses is 0.0.020 inch to 0.030 inch. At these cover thicknesses,the scan reflection coefficient is relatively small in the azimuth scanat the farthest scan angle of 75°. Therefore, this range of coversshould not produce any scan blindnesses in the array in the azimuth scanto 75°.

[0083] In one embodiment, a 0.022 inch thick cover, the closest multipleof 7.4 mils to the optimum thickness using analytic techniques was usedin the design of the radiator. An elevation scan analysis indicated thatthere would be no scan blindness effects with any of the covers at anelevation beam steer of 15°.

[0084] Referring now to FIG. 11 in which like elements of FIG. 10 areprovided having like reference designations, a radiating element 200 andassociated feed circuits are provided from eleven LTCC tape layers202-222, each of the layers having a post-fired thickness typically ofabout 0.0074 inch and having a (stripline) ground plane spacing of0.0148 inch. The element 200 has an element signal port 200 a providedin layer 202.

[0085] The radiating element 200 is provided from the structures to bedescribed below provided in the layers 210-222 as shown. It should benoted that cover layers 218-222 (which may correspond to cover layer 176in FIG. 10) are integral to the radiating element 200. Layer 216 has aground plane 224 disposed thereon. Portions of the ground plane areremoved to form an aperture 226.

[0086] A power divider circuit 228 is coupled through conductive vias230 a, 230 b to a conductive trace 232 and a strip line feed circuit234, respectively. Thus, an elevation feed circuit is interlaced withthe element 200.

[0087] Capacitive windows 240 are formed on layers 214, 216 via bydisposing ground planes material on the layers 214, 216 and providingopenings in the ground planes. Layers 202, 204 and 208 are also providedhaving ground planes 242 disposed thereon. Layers 202-208 are dedicatedto a Butler Matrix circuit while layers 210-216 are dedicated to theradiator and feed circuit.

[0088] The embedded vias 160 in the LTCC are used for forming thewaveguide structure of the radiator in the LTCC while vias 230 a, 230 b,230 c, 230 d are used for transitioning between the circuits on thedifferent layers 202-216. As can been seen in FIGS. 9 and 10, theembedded vias 160 form a waveguide structure and share the same layersas the power divider circuit 228 and the radiator feed circuit 234.

[0089] The LTCC manufacturing flow comprises eight operations which aredefined as: tape blanking, via formation, via filling, conductordeposition, lamination, wafer firing, continuity test, and dicing. Thefollowing is a brief description of each of the eight operations.

[0090] Raw LTCC is supplied in tape form on spools having a standardwidth of either seven or ten inches. Typical tape area per roll rangesfrom 4200 to 6000 sq. in. and is also predetermined at time of order.The blanking of LTCC tape is performed manually with the use of an arborblanking die. Tape is blanked to either a 5″ or a 7″ manufacturingformat size. An orientation hole is also introduced during the blankingoperation which references the LTCC tape's as-cast machine andtransverse directions. This orientation hole will ultimately allow forlayers to be identified and cross-plied in order to optimize totalproduct shrinkage at firing.

[0091] The creation of Z-axis via holes is performed through the use ofa high speed rapid punch system. The system is driven by punch CAD/CAMdata which is electronically down loaded via ethernet directly to themanufacturing work cell. The supplied punch files contain X-Y-coordinatelocations for via formation. Individual tape layers, in either a 5″ or7″ format, are mounted into single layer tape holders/frames. Theseframed layers are subsequently loaded into a handling cassette which canhouse a maximum of 25 LTCC tape layers. The cassette is loaded and ishandled automatically at the work center when respective punch programsare activated. The high speed punch processes via holes in tape layersindividually and ultimately indexes through the entire cassette. Viaholes are formed at typical rates of 8 to 10 holes per second. At thecompletion of via formation for a particular tape layer the cassette isunloaded from the work center, processed tape layers removed, and thecassette is reloaded for continued processing.

[0092] LTCC tape layers which have completed respective via formationoperations require the insertion of Z-axis conductors in order toultimately establish electrical interface with upper and lower productlayers. The via filling operation requires the use of positive pressuredisplacement techniques to force conductive pastes into via formed holesin the dielectric tape. Mirror image stencils are manufactured forrespective tape layers which feature all punched via hole locations;these stencils are fixtured on a screen printing work cell. LTCC tapelayers are soft fixtured onto a porous vacuum stone. The stone isindexed under the stencil where a preset pressure head travels over thestencil forcing deposited conductor paste through the stencil and intothe dielectric tape. Each tape layer is processed in a similar fashion;all layers are dried, driving off solvents, prior to follow onoperations.

[0093] Via filled dielectric tape layers require further processing toestablish X-and Y-axis conductor paths. The deposition of theseconductor mediums provides “from-to” paths on any one LTCC layer surfaceand originate from and terminate at filled via locations. The conductordeposition operation employs the same work center as described in thevia filling operation with the exception that wire mesh, emulsionpatterned screens are substituted for through hole stencils. Thetechnique for fixturing both the screen and the tape product is also thesame. All product layers are serially processed in this fashion untildeposition is complete; again, all layers are dried prior to follow onoperations.

[0094] Prior to lamination all previous tape processing operations occurin parallel with yield fallout limited to respective layer types. Thelamination operation requires the collation and marriage of parallelprocessed layers into series of independent wafers. Individual layers,(layers 1, 2, 3, . . . n), are sequentially placed upon a laminationcaul plate; registration is maintained through common tooling whichresides in all product layers. The collated wafer stack is vacuumpackaged and placed in an isostatic work cell which provides time,temperature, and pressure to yield a leathery wafer structure.

[0095] Laminated wafers are placed on firing setters and are loaded ontoa belt furnace for product densification. Firing is performed in asingle work cell which performs two independent tasks. The primaryoperation calls for the burning off of solvents and binders which hadallowed the tape to remain pliable during the via formation, filling,conductor deposition, and lamination operations. This binder burnoutoccurs in the 350-450 C. range. The wafer continues to travel down thebelt furnace and enters the peak firing zone where crystallization, andproduct densification occurs; temperatures ranging to 850-860C. aretypical. Upon cool down the wafers exit the furnace as a homogenousstructure exhibiting as-fired conditions. All product firing occurs inan air environment. Post firing operations would not require wafers tobe processed through an additional binder burnout steps but would onlyrequire exposure to the 850 C. densification temperatures.

[0096] Continuity net list testing is performed on individual circuitsin wafer form. Net list data files are ethernet down loaded to the netprobe work center and are exercised against respective wafer designs.Opens and shorts testing of embedded nets, and capacitance and resistiveload material measurements defines the bulk work center output. Failuresare root caused to specific net paths.

[0097] Net list tested wafers typically exhibit individual circuitstep/repeat patterns which can range from one to fifty or more on anyone particular wafer. Conventional diamond saw dicing techniques areemployed to singulate and dice circuits out of the net list testedwafers. Common fixturing is in place to handle both 5″ and 7″ firedwafer formats.

[0098] Referring now to FIG. 12, a radar system which may be similar tothe radar systems described above in conjunction with FIGS. 1 and 2respectively for use as a SOD system is shown in greater detail. Ingeneral overview of the operation of the transmitter 22 (FIG. 1), theFMCW radar transmits a signal 250 having a frequency which changes in apredetermined manner over time. The transmit signal 250 is generallyprovided by feeding a VCO control or ramp signal 252 to a voltagecontrolled oscillator (VCO) 254. In response to the ramp signal 252, theVCO 254 generates a chirp signal 256.

[0099] A measure of transmit time of the RF signal can be determined bycomparing the frequency of a received or return signal 258 with thefrequency of a sample 260 of the transmit signal. The rangedetermination is thus provided by measuring the beat frequency betweenthe frequencies of the sample 260 of the transmit signal and the returnsignal 258, with the beat frequency being equal to the slope of the rampsignal 252 multiplied by the time delay of the return signal 258.

[0100] The measured frequency further contains the Doppler frequency dueto the relative velocity between the target and the radar system. Inorder to permit the two contributions to the measured frequency shift tobe separated and identified, the time-varying frequency of the transmitsignal 250 is achieved by providing the control signal 252 to the VCO254 in the form of a linear ramp signal.

[0101] In one embodiment, the VCO control signal 252 is generated withdigital circuitry and techniques. In a preferred embodiment, the rampsignal 252 is generated by a DSP 262 and a digital-to-analog converter(DAC) 264. Use of the DSP 262 and DAC 264 to generate the ramp signal252 is possible in the SOD system of FIG. 12 since, it has beendetermined that by proper selection of the detection zonecharacteristics including but not limited to detection zone size, shapeand resolution, precise linearity of the chirp signal 256 is notnecessary. With this arrangement, the frequency of the transmit signal250 is accurately and easily controllable which facilitatesimplementation of several advantageous and further inventive features.As one example, one or more characteristics of successive ramps in theramp signal 252 are randomly varied (via random number generator 253,for example) in order to reduce interference between similar, proximateradar systems. As another example, temperature compensation isimplemented by appropriately adjusting the ramp signal 252. Yet anotherexample is compensation for non-linearity in the VCO operation. Further,changes to the SOD system which would otherwise require hardware changesor adjustments can be made easily, simply by downloading software to theDSP. For example, the frequency band of operation of the SOD system canbe readily varied, as may be desirable when the SOD is used in differentcountries with different operating frequency requirements.

[0102] An electronics portion 270 of the SOD system includes the DSP262, a power supply 272 and a connector 274 through which signal buses42, 46 (FIG. 1) are coupled between the SOD system and the vehicle 40(FIG. 1). The digital interface unit 36 (FIG. 1) is provided in the formof a controller area network (CAN) transceiver (XCVR) 276 which iscoupled to the DSP via a CAN microcontroller 278. The CAN controller 278has a system clock 279 coupled thereto to provide frequency stability.In one embodiment, the system clock is provided as a crystal controlledoscillator. An analog-to-digital (A/D) converter 280 receives the outputof a video amplifier 282 and converts the signal to digital form forcoupling to the DSP 30 for detection processing. In one embodiment, theA/D converter is provided as a twelve bit A/D converter. Those ofordinary skill in the art will appreciate, however, that any A/Dconverter having sufficient resolution for the particular applicationmay be used. A signal bus 284 is coupled to antenna switch circuits 286,288 in order to provide control signals to drive the switches whichcomprise the switch circuits. Circuits 286, 288 can include switches(e.g. switches 105, 106 of FIG. 5), phase lines (e.g. lines 103 a-103 hof FIG. 5) and a beamforming circuit (e.g. Butler matrix beamformingcircuit 98 in FIG. 5). Also provided in the electronics portion 270 ofthe SOD system is a memory 190 in which software instructions, or codeand data are stored. In the illustrative embodiment of FIG. 12, thememory 190 is provided as a flash memory 190.

[0103] The DSP provides output signals, or words to the DAC whichconverts the DSP output words into respective analog signals. An analogsmoothing circuit 292 is coupled to the output of the DAC in order tosmooth the stepped DAC output to provide the ramp control signal to theVCO. The DSP includes a memory device 294 in which is stored a look-uptable containing a set of DSP output signals, or words in associationwith the frequency of the transmit signal generated by the respectiveDSP output signal.

[0104] The VCO 254 receives ramp signal 252 from the analog smoothingcircuit. The VCO operates in the transmit frequency range of between24.01 to 24.24 GHz and provides an output signal to bandpass filter 296,as shown.

[0105] The output of the VCO 254 is filtered by the bandpass filter 296and amplified by an amplifier 298. A portion of the output signal fromamplifier 298, is coupled via coupler 300 to provide the transmit signal250 to the transmit antenna 18. Another portion of the output signalfrom the amplifier 298 corresponds to a local oscillator (LO) signal fedto an LO input port of a mixer 304 in the receive signal path.

[0106] The switch circuits 286, 288 are coupled to the receive andtransmit antennas 16, 18 through a Butler matrix. The antennas 16, 18and switch circuits 286, 288, and Butler matrix can be of the typedescribed above in conjunction with FIGS. 1-11. Suffice it here to saythat the switch circuits and Butler matrix operate to provide theantenna having a switched antenna beam with antenna beam characteristicswhich enhance the ability of the SOD system to detect targets.

[0107] The received signal 258 is processed by an RF low noise amplifier(LNA) 306, a bandpass filter 308, and another LNA 310, as shown. Theoutput signal of the RF amplifier 310 is down-converted by mixer 304which receives the local oscillator signal coupled from the transmitter,as shown. Illustrative frequencies for the RF signals from the amplifier310 and the local oscillator signal are on the order of 24 GHz. Althoughthe illustrated receiver is a direct conversion, homodyne receiver,other receiver topologies may be used in the SOD radar system.

[0108] A video amplifier 282 amplifies and filters the down-convertedsignals which, in the illustrative embodiment have a frequency between 1KHz and 40 KHz. The video amplifier 64 may incorporate features,including temperature compensation, filtering of leakage signals, andsensitivity control based on frequency, as described in a co-pendingU.S. patent application entitled Video Amplifier for a Radar Receiver,application Ser. No. 09/______, filed on Aug. 16, 2001, and incorporatedherein by reference in its entirety.

[0109] The A/D converter 280 converts the analog output of the videoamplifier 320 into digital signal samples for further processing. Inparticular, the digital signal samples are processed by a fast Fouriertransform (FFT) within the DSP in order to determine the content of thereturn signal within various frequency ranges (i.e., frequency bins).The FFT outputs serve as data for the rest of the signal processor 262in which one or more algorithms are implemented to detect objects withinthe field of view, as described in co-pending U.S. patent applicationentitled Radar Transmitter Circuitry and Techniques, Application No.09/______, filed on Aug. 16, 2001, and incorporated herein by referencein its entirety.

[0110] The radar system includes a temperature compensation feature withwhich temperature induced variations in the frequency of the transmitsignal are compensated by adjusting the ramp signal accordingly. Forthis purpose, the transmitter 22 includes a DRO 322 coupled to amicrowave signal detector 324. The output of the microwave detector iscoupled to an analog-to-digital converter of the CAN controller forprocessing by the DSP. The details of such processing are described inthe aforementioned U.S. patent application Ser. No. 09/______, entitledRadar Transmitter Circuitry and Techniques.

[0111] It should be appreciated that in a preferred embodiment, thereceive and transmit antenna antennas 16, 18 of the sensor system arearranged as a bi-static antenna pair. In other embodiments, however, amonostatic arrangement can be used.

[0112] In one embodiment, the transmit signal path includes a signalsource having an output coupled to an input port of a switch circuithaving a plurality of output ports each of which is coupled through aButler beam forming circuit to a column feed circuit of the transmitantenna. Thus, the number of output ports in the switch circuitcorresponds to the number of columns included in the transmit antenna.In one embodiment, the switch circuit is provided from a coupler circuithaving an input port and a pair of output ports and a pair of switchcircuits, each of the switch circuits having a common port and aplurality of output ports. Each of the coupler output ports are coupledto a one of the switch common ports. Each of the switches has a numberof outputs corresponding to a predetermined number of columns includedin the transmit antenna. In a preferred embodiment, the number of totaloutput ports between the two switches equals the number of columns inthe antenna. Each of the switch outputs are thus coupled to inputs ofthe transmit antenna. With this arrangement, a combined beam transmitarchitecture is provided.

[0113] Similarly, on a receive signal path, the receive antenna iscoupled to a receiver circuit through a Butler beam forming circuit andphase lines which lead from the receive antenna output ports to theinput ports of a switch circuit. The switch circuit can be provided froma coupler and a pair switches as described above in conjunction with thetransmit antenna. By selectively coupling predetermined ones of theswitch circuit input ports to the switch output port, combined beams areprovided. With this arrangement, a combined beam receive architecture isprovided.

[0114] Having described the preferred embodiments of the invention, itwill now become apparent to one of ordinary skill in the art that otherembodiments incorporating their concepts may be used. It is felttherefore that these embodiments should not be limited to disclosedembodiments but rather should be limited only by the spirit and scope ofthe appended claims.

[0115] All publications and references cited herein are expresslyincorporated herein by reference in their entirety.

What is claimed is:
 1. An array antenna comprising: a first plurality ofantenna elements disposed to provide a transmit antenna; a butler matrixbeam forming circuit having a plurality of antenna ports and a pluralityof switch ports with each of the antenna ports coupled to ones of saidfirst plurality of antenna elements; and a first switched beam combiningcircuit having an input port and a plurality of output ports, each ofthe output ports coupled to a corresponding one of the plurality ofinput ports of said butler matrix beamforming circuit.
 2. The antenna ofclaim 1 further comprising: a second plurality of antenna elementsdisposed to provide a receive antenna; a butler matrix beam formingcircuit having a plurality of antenna ports and a plurality of switchports with each of the antenna ports coupled to ones of said secondplurality of antenna elements; and a second switched beam combiningcircuit having a plurality of input ports and an output port, each ofthe plurality of input ports coupled to a corresponding one of theplurality of the output ports of said butler matrix beamforming circuit.3. The antenna of claim 1 further comprising a transmit signal sourcehaving an output coupled to an input of said first switched beamcombining circuit.
 4. The antenna of claim 2 further comprising areceiver coupled to an output of said second switched beam combiningcircuit.
 5. The antenna of claim 1 wherein transmit antenna is providedas an array antenna having a first plurality of antenna columns and saidfirst switched beam combining circuit comprises: a plurality of switchcircuits, each of the switch circuits having an input port and aplurality of output ports with a total number of switch output portsprovided from the combination of said plurality of switch circuitsequals the number of antenna columns provided in the transmit antenna; acoupler circuit having an input port and a plurality of output portsequal to the number of input ports provided from the combination of saidplurality of switch circuits with each of the output ports of saidcoupler circuit coupled to a corresponding one of the input ports ofsaid plurality of switch circuits.
 6. The antenna of claim 5 wherein thenumber of total output ports between said plurality of switches equalsthe number of columns in the antenna.
 7. The antenna of claim 6 furthercomprising phase lines disposed between the switch output ports and theantenna input ports.
 8. The antenna of claim 7 wherein each of saidantenna elements comprises: an array feed circuit layer having aplurality of feed circuits disposed thereon; a radiator layer having afirst ground plane disposed thereon with the ground plane having anaperture therein, said radiator layer disposed over said feed circuitlayer; and a cover layer disposed over said radiator layer; a pluralityof via holes between the first and second ground plane layers to providea cavity in said radiator and feed circuit layers;